Presently, an information processing system in which plural information processing devices communicate through a network is utilized. For example, in a client-server system, a device that offers services (referred to as server) and a device that utilizes the services (referred to as client) communicate through a network. The client transmits a request to the server. The server receives the request and transmits a response according to the request to the client.
The server is capable of receiving plural requests from plural clients. When the number of requests increases, the load of the server increases. If the load of the server becomes excessive, the delay of the response to the client possibly increases. Therefore, a method in which a control device that receives a request of a client and makes access to a server by proxy is provided between the client and the server and the load of the server is suppressed by functions of the control device is being considered.
For example, there has been a proposal of a traffic control device that limits transmission of the request to a server based on the maximum number of couplings that is the allowable maximum number of clients that may simultaneously couple to the server. In this proposal, the maximum number of couplings is set in advance by an operator.
Furthermore, there has also been a proposal of a load control device that limits the number of response-waiting requests that have been transmitted to a server but about each of which a response has not been returned from the server. If the number of response-waiting requests reaches a threshold, the load control device temporarily accumulates a received request in a buffer and waits to transmit the request from the buffer until the number of response-waiting requests falls below the threshold.
There has also been a proposal of database server that calculates the critical multiplicity that is the upper limit value of processing processes for which processing is simultaneously advanced concurrently from the operating status of own hardware and controls the number of simultaneous couplings from clients to the database server while deeming the calculated critical multiplicity as the upper limit.